Tore apart the rear suspension and the trailing arms are out for service. The TA shims were the original 2 hole style and was told to replace with the later model U shape ones for easier alignment. Was also told the backs of those shims will reside in the TA body pocket and require I drill a holes in both sides of the pocket to run a bolt through to secure them from moving.
Any insight and/or pictures of this project would be greatly appreciated.

 

did this job on my 68 when I rebuilt the trailing arms. As you say the 68 had the hole on each end trailing arm shim so the only way to swap shims was to pull the trailing arm out. Although some say, alignment men back in the day just bent the trailing arm, ugh!

So you need to drill a hole on each side of the trailing arm pocket and install the long cotter pin, photos:


I thought the biggest part of this PITA job was access and this helped:

I think it might be best to wait until you get the TA back and trial install with some shims to get the new shim cotter pin hole in just the right place.

Hopper12 (?) did this job recently too, so you might do a search here to learn more.

Hope this helps.

 

Thanks for the reply. Was thinking a through bolt (under the TA) similar to the one in the trailing arm bushing was to be used. I guess a cotter pin in each side through the shim and pocket side would do the job of holding them in place.
I don’t have a 90 degree drill adapter, but can understand one would make the job much easier. Always looking to buy new toys.
As for the shims, thinking to replace with SS. They only come in 3 thicknesses? My current non SS ones appear to be 3 different thicknesses.

 

You drill the hole because the cotter pin is long and goes in one side and out the other side of the frame.
Not to be confused with the small cotter pin in the bolt.

One pack of shims in whatever size they offer will be enough. You can use the 'trailing arm' bolt as a guide the locate the hole position, you don't want the T/A installed to do this.

 

So, 1 large cotter pin for each set of shims….4 total.
Agree, locating and drilling the cotter pin holes will be easiest with the TA out. Assume you align the shims against the TA bolt and clamp the shims to the pocket side to hold tight during drilling?

 

Another idea. I can’t take credit for it I read it on the forum.

use 1 style old 2 hole shim on either side of the bolt. You can put this is and it never has to come out for alignment. Use the updated slotted shims for alignment then wire tie them to the 2 hole shim. Can’t come out then.

I will also say there are likely plenty of c2s and early c3s with slotted shims and no cotter pin. Ans they haven’t fallen out

 

Here's the end of the T/A bolt with the castellated nut and small cotter pin.
You can see the end of the big cotter pin and the shims in the pocket.
Withy the T/A bolt installed and a shim installed on the outside of the bolt you'll find where the hole goes.

On the final installation install the pin from the inside to the outside not the way you see it in the picture.

 

Thanks for the photo and additional ideas on using some old hole shims to hold the new slotted shims in place.
How tight do you make the castellated nut to assure it holds the TA in place without binding up the bushing?

 

Agree, you do not want to drill your long cotter pin holes with the TA installed and I did not either. I did trial install the TA though, as I said, to see how it all fits and to locate your new holes. I suppose you could stick a pivot bolt in there too to locate the hole w/o the TA though. After you finish the install you want to torque the pivot bolt to 45 to 55 ft lbs at ride height (per 68 AIM). So I lowered the rear to get weight on the rear tires as normal. and then checked to see how much space existed in the bottom of the rear pocket, then shimmed to maintain that space and jacked back up to do the final torque on the pivot bolt. The pocket needs to be packed tight with the correct amount of shims on each side for whatever alignment is correct before you do the final torque. Looks to me like the TA actually moves in the rubber as both bushings end up tight in the TA and in the pivot bolt/shim pack.

There are a number of posts here and on the internet on this whole job, Great photos above too. Hope this helps.

 

As mentioned the photo shows the shims secured within the TA pocket. Since the original shims extend outside the TA pocket, I assume the replacement shims are shorter as well as slotted.
Was thinking to use the original shims and cut out the holes to create slots. That said would the shims extending outside the TA pocket create a problem with the cotter pin drilling and placement?

 

Just buy the shims that 20mercury posted, they will fit correctly and be secured in place with the big cotter pin.

Ob final assemble the 'pocket' will be packed tightly with shims so that you do not crush the 'pocket' when you tighten the nut and bolt.

 

Will double check but I think the original OEM 2 hole shims are the same length as the new slotted shims. The newer slotted shims just slide up pass the center line of the OEM shim pivot bolt hole.

Couple of thoughts; first, has your rear end been aligned as the shim size might change with a new alignment?

2nd if you believe your alignment is good with the original shims, you could cut the original shims to the slot shape by seeing how far you need to cut with a trial fit with a pivot bolt as Peterbuilt says. Or using a newer slotted shim as a pattern. That will be a lot of cutting compared to how cheap TA shims are. I last used some steel ones and painted them if you do not want to splurge for SS.

My 2 cents. Will see if I can find my old 2 hole 68 shims and compare to slotted.

BTW, good advice from Peterbuilt, on the first TA rebuild I did, I did not pack the pocket with shims and fortunately realized before doing any damage. the pocket will bend in when torqueing the pivot bolt if the pocket is not packed

 

Honestly, I bought the car Oct 2019 and haven’t driven it on the road yet. Full interior rebuild followed by front and rear rebuilds has kept me busy. Not sure of the cars alignment, but the TA’s were fully packed with shims and in pretty good shape when I took them out. Planning on reinstalling the rebuilt TA’s with the original shims cut to be slotted or new slotted shims that will allow a shop to easily pull them to do a full 4 wheel alignment.
The bushing bolt will be fully packed with shims regardless of using old cut shims or new slotted shims eliminating any potential pocket crushing. Was just concerned when I slot cut the old shims the back end would continue to be outside the pocket and potential back out regardless of the cotter pin. Makes sense the new shims might be the same length with deeper slot cuts that allow the back ends to tuck inside the pocket eliminating any potential back out regardless of the cotter pin.

 

Sounds like a great ride, 68 Corvettes are my favorite! Post photos when you are ready!

 

Finally found my old 68 trailing arm shims which I am pretty sure are original.

FWIW:

The 2 hole original 68 OEM trailing arm shims are 4-3/4" long and 1-1/4 wide.

The newer 69+ trailing arm shims are 4-1/2" long and 1-1/4" wide so the newer shims are a 1/4" shorter.

 

I made the Guy who aligned my C3 REAL happy when he saw I had brought four packs of new Stainless shims for the C3 with me. Both of my trailing arms were done by Van Steel and have their warranty. I had the tech do a 4 wheel alignment and he literally removed all the old shims and started over centering the differential and after several hours (4+) and I got the best $99 4 wheel alignment I ever paid for.

My C3 had never handled as well as it did when he was finished. I was amazed at the difference after the alignment. So I took my C3 home and the next day I brought over my C4, I wasn't going to miss out on this kind of service. I also tipped him more than the alignment cost by itself just for the C3 alignment. He deserved it as it was important to him to do the job the right way!

 

Thanks for the reply. TA’s are currently out with Bairs for the rebuild and I will purchase the SS slotted shims for the reinstall. Just hope I can find a good C3 service station and guy to do the alignment with that dedication.

 

Hi, Just saw this thread and I did do this recently on my '68 (good memory Mercury!). Batesgar, you've received a lot of great info from the always helpful members of the forum. A couple of things I found:
* As stated, easier to do with the TAs out, but you could do it with them in if you jack them up out of the way I suppose.
* I used cobalt drill bits, dipped them periodically in a cap with WD40 in it, and they drilled the relatively thick frame material no problem. The right drill bits and some lubrication/coolant make a big difference.
* The pic from Peterbilt is a great one too - shows you where to make the holes. I put a TA bolt in place while the TAs were out to help locate the shims just to be sure.
* I now wish I had drilled my holes just a bit lower, but they are working just fine because the holes thru the shims are large and allow the shims to drop lower than the holes.
* A couple of long cotter pins come with each set of shims. I bought two sets so I had enough different thicknesses and a couple of extra cotter pins.
* Drive the shims in on each side, trying to come close to matching the number of shims you took out on each side. I wasn't able to put in the same number of shim as I took out - probably because the TA bushing was a bit longer than the old one. Make sure you drive them in before you drive your car to the alignment shop.
* I had a bit of trouble getting the shims in on the inside of the newly rebuilt TAs, but jacking up the TA did the trick and I was able to get them in. In hindsight, I would have been better off driving the shims in prior to installing the spring, camber stuff, etc.

Your alignment guy will thank you for the change. This is one of the crazy C3 '68 only gifts that we deal with.

I just got mine started up on Monday, and have driven it around the block a couple of times because I did lots of other things to the car and I want to be sure it's all good before I take it in for alignment.

Best! Paul

 

Thanks for the advice. I’ve seen in other threads that the inside shims determine toe, while the outside shims are just fillers. That said, if I can’t get the same amount of shims back in place due to TA bushing differences, I should make sure the inside ones are the same as what came out.